1. Technical Field of the Invention
The present invention relates to a telecommunications network and, in particular, to the optimal routing of terminating calls towards a mobile station.
2. Description of Related Art
With the advent and development of mobile telecommunications systems, telecommunications users are no longer physically bound to wireline terminals or fixed locations for telecommunications network communications. Using the added capabilities of roaming and interoffice handoffs, mobile subscribers may travel between multiple Public Land Mobile Networks (PLMNs) utilizing the same telephone number and the same mobile station to originate outgoing calls and to receive incoming calls. Thus, a mobile subscriber may access telecommunications service from multiple locations utilizing multiple service providers with any incurred fees being charged to a single subscription. Furthermore, calling parties do not necessarily have to know where the mobile subscriber is physically located in order to establish a call connection. Data signals between visitor location registers (VLRs) and a home location register (HLR) automatically update and store subscriber information, in particular subscriber location information, enabling the network to reroute incoming calls to the appropriate mobile switching center (MSC) serving the roaming mobile subscriber. Furthermore, regardless of which MSC is currently serving the mobile station, the VLR associated with the serving MSC communicates with the HLR assigned to the mobile station to retrieve the requisite subscriber data, including subscriber feature data and billing data, and provides uniform mobile service to the mobile station.
Conventionally, if a mobile station associated with a New York (N.Y.) mobile telecommunications network is traveling in Los Angeles (L.A.), an incoming call towards the roaming mobile station is first routed to the gateway mobile switching center (GMSC) serving the N.Y. public land mobile network (PLMN) associated with the mobile station. Thereinafter, the N.Y. GMSC performs an interrogation with the home location register (HLR) associated with the mobile station to determine the current location of the roaming mobile station. Upon determining the identity of the L.A. mobile switching center (MSC) currently serving the N.Y. mobile station, the received incoming call is rerouted by the N.Y. GMSC to the serving L.A. MSC to enable a speech connection between the calling party terminal and the roaming mobile station.
Accordingly, if the calling party is originating a call setup signal from L.A., a first trunk call connection between the L.A. telecommunications network and the GMSC serving the home PLMN is initially established and then a second trunk call connection between the GMSC back to the L.A. MSC currently serving the mobile station is established. As a result, a "tromboning" of trunk call connections through N.Y. is performed in order to establish a call connection between two telecommunications subscribers both located in L.A.
Such "tromboning" trunk call connections are disadvantageous for a number of reasons. Unnecessary trunk connections have to be established and maintained in order to enable two subscribers who are locally located to communicate with each other and result in unnecessary seizure of valuable network resources. Additionally, even though the called party mobile station is receiving an incoming call from a calling party terminal located within the same local access transport area (LATA), such as L.A., the called party mobile station has to incur long distance charges for forwarding the call connection from his or her home PLMN back to the visited PLMN. Furthermore, the calling party also has to incur long distance charges to N.Y. for calling another mobile station located within the same PLMN.
Accordingly, there is a need for a mechanism to enable the serving mobile telecommunications network to perform optimal routing of a mobile call towards a roaming mobile station.